Field of the Invention
Esters of unsaturated carboxylic acids can be produced by well known ester exchange reactions. In this type of reaction catalysts are generally used such as sulfuric acid and paratoluenesulfonic acid and alcoholates such as alkali metal alcoholates, aluminum alcoholates and titanium alcoholates. However, these catalysts have their drawbacks. For instance, when an acid catalyst such as sulfuric acid is used, the reaction rate is slow and the production of undesired polymer by-product increases. Furthermore, when a primary alcohol is used as a starting material, an ether by-product is produced. When a secondary alcohol is used as a starting material, a portion of the alcohol is dehydrated and an olefin is formed as a by-product. Other problems exist in that the ester exchange, the reaction will not proceed with some kinds of alcohols, and the reaction apparatus frequently corrodes.
On the other hand, when an alkali metal alcoholate such as sodium methylate is used as the catalyst, not only do such undesirable secondary reactions simultaneously occur such as the by-production of an additional reaction product, the by-production of an alkali metal salt and an anionic polymerization reaction, but also complicated procedures are necessary such as the continuous addition of catalyst to the reaction mixture as it loses its activity with the passage of time and the thorough prior dehydration of the catalyst because the catalyst loses its activity with time by reacting with water in the reaction system. Further, the catalyst must be washed with water and removed from the reaction mixture to prevent polymerization before the obtained product is separated from the reaction medium such as by distillation. This is a complicated process step. In addition the process necessitates the treatment of waste water from the reaction.
When aluminum alcoholate or titanium alcoholate is used as the catalyst, not only do the same drawbacks exist as when alkali metal alcoholates are used, but the catalysts lose activity with the passage of time and by the influence of water, but also the catalytic activity of these catalysts will diminish to a level less than the alkali metal alcoholate catalysts. Consequently, the amount of catalyst must be increased or the reaction time must be lengthened. Because of these problems with the conventional catalysts, a need continues to exist for an improved catalyst for ester exchange reactions which overcomes the deficiencies of the conventional catalysts.